Infrasense scans bridge decks in Wisconsin to evaluate condition

Infrasense Inc. has completed subsurface investigations for 21 bridge decks in Wisconsin’s southwest region. A suite of nondestructive tests was performed for each bridge deck inspection, including a ground penetrating radar survey, infrared thermography evaluation, and impact echo testing. These tests provided a condition assessment of the reinforced concrete bridge decks without requiring any cores or exposed rebar, and with minimal disruption to traffic flow.

Since 2007, Infrasense has surveyed more than 300 bridge decks across Wisconsin using its multi-phase approach. After completing a quick and simple preliminary (Level 1) bridge deck analysis, many are found to be in good condition and require no further analysis. Those found to have more significant deterioration levels are mapped in detail (Level 2), providing data to accurately plan, program, and budget maintenance and rehabilitation.

Ground Penetrating Radar (GPR) data is collected to estimate rebar depth and identify corrosion. The GPR data is collected in a series of lines spaced 3 feet transversely across the width of the deck, with each line representing a cross sectional slice of the deck at a particular offset. Decks in good condition consist of strong and uniform radar reflections from the rebar. GPR data with weak and inconsistent reflections indicate rebar-level bridge deck deterioration.

The infrared data is collected in a series of passes across each deck, with each pass covering a deck width of between 12 and 15 feet.

For a typical interstate deck with two lanes and left and right shoulders, the survey is carried out in four passes – one in each lane and one in each shoulder. The survey produces a series of infrared images collected every foot of vehicle travel.

During the survey, selected areas that appear delaminated in the IR image are manually sounded to confirm the presence of delamination. Because many of these decks have overlays, the reinforcing can be 4-5 inches from the surface, and sounding is not always capable of detecting delamination at this depth. For those locations where the delamination cannot be confirmed by sounding, testing is carried out using the Impact-Echo method. By analyzing wave frequencies through the concrete, the impact-echo equipment is capable of detecting delamination at any depth throughout the thickness of the deck.

Many agencies apply GPR and IR separately as tools for bridge deck assessment, or use only one preferred method. Each method has specific strengths and weaknesses, and Infrasense uses a combination of both to create a more effective bridge deck condition assessment. By combining IR and GPR surveys and using a two level analysis approach, the maximum amount of information can be obtained for the least cost.